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%I #14 Sep 08 2022 08:46:24
%S 1,2,3,4,5,11,7,8,9,17,11,12,13,23,23,25,17,18,19,41,31,22,23,59,25,
%T 41,27,39,29,71,31,32,47,53,47,36,37,59,39,89,41,77,43,83,45,71,47,75,
%U 49,50,71,97,53,95,71,95,79,89,59,167,61,77,103,64,83,119
%N Greatest k such that sigma(k) = sigma(n).
%H Amiram Eldar, <a href="/A325651/b325651.txt">Table of n, a(n) for n = 1..10000</a>
%e a(6) = 11 because sigma(6) = sigma(11) = 12.
%t a[n_] := Block[{s = DivisorSigma[1, n], k}, k=s; While[ DivisorSigma[1, k] != s, k--]; k]; Array[a, 66] (* _Giovanni Resta_, May 20 2019 *)
%o (Magma) [Max([k: k in[1..10000] | SumOfDivisors(k) eq SumOfDivisors(n)]): n in [1..100]]
%o (PARI) a(n) = {my(s=sigma(n)); forstep(i=s, 1, -1, if (sigma(i) == s, return(i)););} \\ _Michel Marcus_, May 12 2019
%Y Cf. A000203, A275987 (least k such that sigma(k) = sigma(n)).
%Y See A070242, A325652 and A325653 for number, sum and product of such numbers k.
%K nonn
%O 1,2
%A _Jaroslav Krizek_, May 12 2019
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